Basic aluminum chlorosulfate flocculating process

ABSTRACT

A novel basic aluminum chlorosulfate, well adopted for the improved purification of aqueous media, has the formula 
     
         Al.sub.n OH.sub.m (SO.sub.4).sub.k Cl.sub.3n-m-2k 
    
     and characteristic basicity, Al/Cl ratio, molecular weight and hydrodynamic diameters.

This application is a divisional, of application Ser. No. 242,608, filedSept. 8, 1988, now U.S. Pat. No. 4,981,673 which is a divisional ofapplication Ser. No. 884,964 filed July 14, 1986 abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel basic aluminum chlorosulfate, aprocess for the preparation thereof and its use as a coagulating orflocculating agent for the treatment of aqueous media.

2. Description of the Prior Art

A wide variety of coagulating agents suitable for use in the treatmentof effluents, residual waters or waste waters are known to this art.Ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate andferric chlorosulfate are representative.

More especially representative are the aluminum sulfates, andspecifically basic aluminum chlorosulfates.

The latter compounds are indeed effective. Nonetheless, more recently ademand has arisen for materials which leave lesser and lesser amounts ofaluminum residues in the treated waters. Furthermore, the searchcontinues for more versatile and flexible such materials.

SUMMARY OF THE INVENTION

Accordingly, a major object of the present invention is the provision ofa novel basic aluminum chlorosulfate well adopted as an improvedcoagulating agent for the treatment of aqueous media, and whereby theresidual aluminum content of the treated waters is maintained quite low.

This invention also provides a facile process for the preparation of thetitle compounds, and provides for the production of basic aluminumchlorosulfates adopted to form sludges having high coefficients ofcohesion.

Also provided hereby are certain solutions of basic aluminumchlorosulfates which are both colorless and only slightly turbid.

Briefly, the present invention features novel basic aluminumchlorosulfates having the following general formula

    Al.sub.n OH.sub.m (SO.sub.4).sub.k Cl.sub.3n-m-2k

wherein the basicity thereof, or the ratio m/3n×100, ranges from about40% to about 65%, the ratio of Al equivalent/Cl equivalent ranges from2.8 to 5, and the apparent molecular weight MA, measured by conventionallight diffusion, and the apparent hydrodynamic diameters φZ and φWthereof, measured by the quasi-elastic diffusion of light, are asfollows:

    MA=7000 to 35000

    φZ (Å)=350 to 2500

    φW (Å)=200 to 1200

The basic aluminum chlorosulfate according to the invention is alsocharacterized by the process for the preparation thereof. A basicaluminum chlorosulfate comprising material having the general formula:

    Al.sub.n OH.sub.m (SO.sub.4).sub.k Cl.sub.3n-m-2k

is conveniently prepared by (i) slurrying calcium chloride with calciumcarbonate (chlorocarbonate slurry), (ii) contacting the chlorocarbonateslurry with aluminum sulfate, and (iii) separating the mixture ofreaction into a calcium sulfate cake and a filtrate which comprises saidbasic aluminum chlorosulfate, wherein the amounts of the chlorocarbonateslurry and the aluminum sulfate are such that a ratio m/3n×100 rangingfrom about 40% to 65% is provided in the resultant basic aluminumchlorosulfate, as is an Al equivalent/Cl equivalent ratio of from 2.8 to5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

More particularly according to the present invention, the subjectprocess for the preparation of basic aluminum chlorosulfate comprises(i) a stage of producing a calcium chloride and calcium carbonate slurry(chlorocarbonate slurry}, (ii) a stage of contacting the chlorocarbonateslurry with aluminum sulfate, followed by (iii) a stage of separatingthe reaction mixture thus obtained, whereby a calcium sulfate cake and afiltrate containing the basic aluminum chlorosulfate are provided.

In the following description, this process shall be identified as the"general" process for the production of a basic aluminum chlorosulfateaccording to the invention.

The basic aluminum chlorosulfate of this invention as been definedhereinabove.

Its basicity advantageously ranges from 40 to 60%, nd more particularlyfrom 45 to 56%. The chlorosulfate according the invention also has an Alequivalent/Cl equivalent ranging from 2.8 to 5, and more particularly3.2 to 4. Finally, it is advantageous that the chlorosulfate of theinvention have a proportion of desulfation (the proportion representingthe ratio of the amount of sulfate eliminated to that initially presentin the starting material aluminum sulfate) ranging from 70 to 90%,preferably from 70 to 85% and more particularly from 75 to 82%.

These three parameters, i.e., basicity, Al/Cl ratio as defined above andthe degree of desulfation, and corresponding to the values given above,impart excellent stability to the chlorosulfate of the invention. Thisstability is manifested by the time in storage of the chlorosulfate inthe absence of any precipitation; in the present case, such stabilitymay extend to several months at ambient temperature.

The chlorosulfate of the invention also has a high apparent molecularweight ranging from 7000 to 35,000 and more particularly from 22,000 to32,000. This weight is determined by conventional light diffusion on abasic aluminum chlorosulfate according to the invention, in an aqueoussolution having an Al₂ O₃ concentration of 8.3% by weight. The weightdetermination is measured immediately after the preparation of thesample by the process of the invention. The measurement is carried outusing medium intensities diffused at an angle of 90°.

The hydrodynamic diameters of the chlorosulfates are measured by thequasi-elastic diffusion of light using an identical Al₂ O₃concentration.

The chlorosulfates according to the invention may have hydrodynamicdiameters for φW weights, expressed in Angstroms, of from 200 to 1200,more particularly from 800 to 1100. As regards the hydrodynamicdiameters on the order of φZ, expressed in Angstroms, these may rangefrom 350 to 2500, more particularly from 1500 to 2200.

Lastly, NMR measurements for monomeric aluminum content evidenced that15 to 25% of the aluminum is in monomeric form in the basic aluminumchlorosulfate of the invention, the remainder of the aluminum being inpolymer form.

The chlorosulfates according to the invention may be characterized in anequivalent and alternative manner by their average molecular weightM_(w) and their average real hydrodynamic diameters φZ and φW.

These values are measured in conventional manner, by extrapolating tozero concentration, the curves respectively representing the reciprocalof the apparent molecular weight MA and the reciprocal of the apparenthydrodynamic diameters as a function of the concentration of thepolymerized fraction of the basic aluminum chlorosulfate studied. Thecorrespondence between the average real value and the apparent value ofthe molecular weight is given by the Debye equation:

    1/M.sub.w =1/Ma+Bc

wherein c is the concentration of the basic aluminum chlorosulfatesolution and B a constant (virial coefficient).

In the same fashion, the interpretation of the correllograms (see, forexample, Pusey, Photon Correlation and Light Beating Spectroscopy, page387, Plenum Press (1973), makes it possible to determine for eachconcentration, the apparent hydrodynamic diameters φZ and φW, and, byextrapolation to zero concentration, the average real diameters.

Advantageously, as the diluent for the preparation of samples ofdifferent concentration, the supernatant liquid is used which isobtained by the extended ultracentrifugation of solutions of the basicaluminum chlorosulfates of the present invention. This supernatant iscompletely compatible with polymer solutions and, as a practical matter,no longer diffuses light.

The correspondence between the system of real values and the system ofapparent values given above enables characterization of thechlorosulfates of the invention by an average molecular weight of from10,000 to 30,000 and more particularly from 19,000 to 30,000. Similarly,the real average hydrodynamic diameters on the order of φZ range from 90to 450 Å and more particularly from 100 to 150 Å, and those on the orderof φW range from 50 to 300 Å, more particularly from 60 to 80 Å.

The process for the preparation of the chlorosulfates according to theinvention will now be more fully described.

In a first stage, a slurry is prepared from a mixture of calciumcarbonate and calcium chloride. The amount of calcium chloride isdetermined as a function of basicity and the extent of desulfationdetermined for the final product.

This slurry is subsequently contacted with aluminum sulfate, typicallyin the form of an aqueous solution thereof. In general, a solutionhaving 8.3% by weight of Al₂ O₃ is used.

The addition of the slurry is carried out over a period of time varyingtypically ranging from 50 min to 4 hr. The addition is regulated such asto limit to the maximum the carbon dioxide foam which is formed duringthe reaction.

The reaction mixture is agitated (nonshearing agitation) and maintainedat a temperature typically ranging from 35° C. to 50° C. A highertemperature may initiate parasitic reactions. A lower temperature maycause difficulties during the subsequent filtration. In one particularembodiment of the invention, following the addition of all of thecalcium chloride and calcium carbonate, an aging and cooling stage ofthe reaction medium is advantageously carried out.

In this case, the reaction mixture is allowed to cool to a temperaturethat usually ranges from 5° C. to 20° C. During the aging, the mixtureis maintained under nonshearing agitation.

The aging period typically extends from 45 min to 3 hr.

It may also be desirable to extend the aging stage by a further stagewherein the temperature of the reaction mixture is maintained, forexample, at from 5° C. to 20° C. This temperature may be maintained for15 min to 1 hr, for example.

Following the reaction and the optional aging and cooling stage, thereaction medium is separated. The separation may be carried out by anyknown means, in articular by filtering, centrifugation, draining ordecantation. Preferably, filtration is used. It may also be advantageousto use a filter under pressure.

After filtration, a cake essentially consisting of calcium sulfate and afiltrate constituting the end production and containing the basicaluminum chlorosulfate according to the invention, are recovered.

The chlorosulfate product may be advantageously used for the treatmentof an aqueous medium, such as, for example, drinking water, industrialfeed water or waste waters.

In this case, the final product is added to the aqueous medium invariable proportions, as a function of the water to be treated.

In such an application, the product of the invention makes it possibleto realize a particularly low amount of residual aluminum in the mediumtreated. Furthermore, while it is generally necessary with the prior artmaterials to treat aqueous media at pH values less than 8 to provide anacceptable amount of residual aluminum, this is not necessary with thefinal product of the present invention. This makes the use thereof muchmore flexible.

It has also been determined that the novel basic aluminum chlorosulfatesof the invention have improved properties, in particular concerning thecoefficient of cohesion of slurries contained in aqueous media treatedwith the subject chlorosulfates.

It is known that the principal devices intended for the treatment ofaqueous media consist of gravity clarifiers based on the principle ofsedimentation, i.e., the elimination of materials suspended in the waterby gravity decantation.

The setting basin thus contains, at its base, a bed of sludge and, asthe supernatant liquid, a clarified liquid effluent which is removed byoverflow.

However, in view of the operating and production conditions of this typeof installation, large scale variations in the speed of intake of thewater to be treated in the settling facilities may be noted.

This has the effect of disturbing the decantation, and in certain casesto adversely affect the quality of the water decanted, if thecoefficients of cohesion of the resultant sludges are inadequate.

It is now understood that these variations within a given installationare acceptable, only if the solidity of the bed of sludge in thesettling zone is sufficient.

Stated differently, with a given cohesion of the sludge bed, the higherthe speed of the overflow desired, the less sedimentation will takeplace under acceptable conditions.

To resolve this problem, provided hereby is an improvement in themanufacturing process described above, characterized in that thechlorocarbonate slurry is reacted continuously with the aluminumsulfate.

It has now been discovered that such an improved process enablesproduction of materials which, quite unexpectedly and surprisingly, formsludges having significantly improved coefficients of cohesion.

This embodiment differs essentially from the process described above byits continuous nature.

By "continuous process" is intended that the flow of the startingmaterials (chlorocarbonate and aluminum sulfate slurry), the nature ofthe intermediates in the course of conversion (aluminum sulfate underbasification) and the final products withdrawn (aluminum sulfate havingthe desired basicity, admixed with the gypsum formed) are in steadystate.

The contacting of the chlorocarbonate slurry with the aluminum sulfatemay be carried out in a single phase.

However, in a preferred embodiment of the invention, the basification ofthe aluminum sulfate is effected in at least two successive phases byreacting the chlorocarbonate slurry with the aluminum sulfate, underconditions such that the basicity of the aluminum chlorosulfate presentin the reaction medium existing after each basification phase, increasesfrom the first to the last phase.

In actual practice, the successive basification reactions of thealuminum sulfate take place in at least two reactors placed in series.

The number of reactors is theoretically unlimited, but is controlled byeconomics. Advantageously, two reactors are used.

In another preferred embodiment of the invention, in the first phase allof the aluminum sulfate is reacted with a first fraction of thechlorocarbonate slurry, whereupon the remaining fractions of thechlorocarbonate slurry are successively reacted with the reaction mediumissuing from each of the preceding phases, whereby, in the last phase,the aluminum chlorosulfate of the desired basicity is obtained.

Thus, in actual practice, an initial solution of Al₂ (SO₄)₃ iscontinuously charged into the first reactor alone, into which thechlorocarbonate slurry is also introduced; this reaction medium thenserves as feed for the second reactor, into which the chlorocarbonateslurry is again introduced in a manner such as to increase the basicityof the aluminum chlorosulfate contained in the reaction medium issuingfrom the first reactor, and the operation is repeated in all of thesuccessive reactors such that the aluminum chlorosulfate having thedesired basicity is recovered from the last reactor.

In another embodiment of the invention, the principal flow of thechlorocarbonate slurry is divided into n fractions which are distributedin parallel over the n reactors, such that the average basicity of thealuminum chlorosulfate present in the reaction medium successivelyissuing from each reactor progressively increases, up to the finalbasicity desired at the outlet of the last reactor.

Generally, the operation is carried out in a fashion such that thebasicity of the aluminum chlorosulfate present in the reaction mediumemanating from the first reactor ranges from 15 to 35%.

The basification reactors are moderately agitated (nonshearingagitation) to maintain the homogeneity of the reaction medium.

The reactors are maintained at a temperature generally ranging from 35°C. to 50° C.

As in the case of the general process, the reaction medium exiting thelast reactor may be subjected, prior to separation by filtration, to anaging and cooling stage.

The basic aluminum chlorosulfate solutions provided hereby have improvedproperties, in particular relative to their coloration and turbidity.

In effect the basic aluminum chlorosulfate obtained after the filtrationof the reaction medium may have, in certain cases, a color extendingfrom a very deep brown to yellow, and, on the other hand, a turbiditygreatly exceeding one hundred NTU units.

This turbidity, which may be redhibitory, is due to a particularly highproportion of solids in suspension, in particular relative to gypsumfines which pass through the filter during the filtration stage, and itis conceivable that the strong coloration of the product solutions iscaused by colorant impurities based in particular on iron or humicsubstances, with the nature and amount of these colorant impuritiescertainly varying as a function of the quality of the startingmaterials.

The present improvement thus features a process for the preparation ofbasic aluminum chlorosulfate solutions, both colorless and having lowturbidity, the latter being less than about ten NTU units.

For this purpose, an improvement in the general processes set forthabove is provided, said improvement being characterized in that, in atleast one of the aforementioned stages or phases, together orseparately, at least one adsorbing agent and at least one flocculatingpolyelectrolyte, either nonionic or cationic, are added.

Consistent with such improvement, final products are obtained that are,surprisingly, both colorless and clear.

The improvement is thus characterized in that an adsorbant and anonionic or cationic flocculating polyelectrolyte are used.

Exemplary of the adsorbants suitable for use according to the presentinvention, particularly representative are activated carbon, activatedalumina, alumino-silicates, silica gels, magnesia and clay.

The adsorbants described above may be used either alone or incombination.

In a preferred embodiment of the invention, activated carbon is used.

The adsorbant may be introduced at any level in the production of thesubject basic aluminum chlorosulfate, but always prior to the separationstage, in particular filtration.

It is found, however, that it is particularly advantageous to introduceit during the stage of the preparation of the chlorocarbonate slurry.The most effective decoloration was observed in this case.

The amount of the adsorbing agent to be introduced is not critical andmay vary over wide limits, depending upon the desired final quality ofthe product.

In the particular case wherein activated carbon is used, usually anamount of from 0.5 to 10 kg thereof, is employed per ton of the aluminumsulfate to be basified. This amount preferably ranges from 1 and 5 kg ofactive carbon/ton of aluminum sulfate.

The polyelectrolytes suitable for use according to the present inventiontypically are high molecular weight polymers, said molecular weightsgenerally being greater than one or several millions.

As regards polyelectrolytes of the nonionic type, particularlyrepresentative are the polyacrylamides, polyethylene oxides,polyvinylpyrrolidones and polyvinyl alcohols.

Preferably, the polyacrylamides are used.

Representative polyelectrolytes of the cationic type suitable for use inthe present invention are, in particular:

(i) Neutral polyamines and quaternary polyamines. More particularly, thepolyalkyleneamines and neutral or quaternary polyhydroxyalkyleneaminesare exemplary For example, the following homopolymers are especiallysuitable: polyethyleneamine, 2-hydroxy-1-propyl-N-methylammoniumpolychloride, 2-hydroxy-1-propyl-l,N-dimethylammonium polychloride,2-vinylimidazolinium polyhydrogenosulfate and diallyl-dimethyl-ammoniumpolychloride. The copolymer formed from acrylamide anddiallyl-dimethyl-ammonium chloride is also suitable;

(ii) Polyaminoacrylates and polyaminomethacrylates and more preciselypolydialkylaminoalkylacrylates and polydialkylaminoalkylmethacrylates.As an example, neutral or quaternarypoly-N,N-dimethylaminoethylmethacrylate is very suitable, both in thehomopolymer form or as a copolymer with acrylamide;

(iii) Polyaminoacrylamides and polyaminomethacrylamides, and moreprecisely polydialkylaminoalkyl acrylamides or methacrylamides. Asexamples, poly-N-dimethylaminopropylmethacrylamides andpoly-N-dimethylaminomethylacrylamides are representative.

It will be appreciated that this list of polyelectrolytes is exemplaryonly and not intended as limiting. All of the polyelectrolytes, takenindividually or in admixture, with the exception of the anionic typewell known to this art, are in effect suitable for use in the presentinvention.

However, a polyelectrolyte of the nonionic type is preferably used, asit has been noted that same lead to better results, even if used insmaller amounts.

As was the case with the adsorbing agents, the polyelectrolyte may beintroduced during any of the stages for the production of the basicaluminum chlorosulfate, but always prior to the separation stage, inparticular filtration.

However, in another preferred embodiment of the invention, theflocculating polyelectrolyte is introduced into the reaction mixtureobtained after the contacting of the chlorocarbonate slurry with thealuminum sulfate, immediately prior to the separation stage, inparticular the filtration.

In an even more preferred embodiment of the invention, the flocculatingpolyelectrolyte is advantageously introduced into said reaction mediumafter an aging stage, such as that described under the general process.

The amount of the flocculating agent to be introduced depends upon thequality desired of the final basic aluminum chlorosulfate solution.However, it was unexpectedly and surprisingly discovered that, in allcases, particularly low amounts of the flocculating agents provide thedesired results.

In actual practice, amounts ranging from 1 to 100 g of polyelectrolytesper ton of the reaction medium are used, i.e., per ton of the mixtureobtained after contacting the chlorocarbonate slurry and the aluminumsulfate to be basified (mixture of basic aluminum chlorosulfate andgypsum).

After introducing the adsorbant and the flocculating polyelectrolyte, asdefined in the description above, and filtering the reaction medium, aclear and colorless basic aluminum chlorosulfate (turbidity may be lessthan 10 NTU) solution is obtained.

Furthermore, aluminum yields appreciably higher than those obtained bythe general process, are observed.

The aluminum yield is defined as the weight ratio of the aluminumpresent in the form of basic aluminum chlorosulfate (final product) andthe amount of the aluminum introduced in the form of aluminum sulfate.

In order to further illustrate the present invention and the advantagesthereof, the following specific examples are given, it being understoodthat same are intended only as illustrative and in nowise limitative.

EXAMPLE 1

This examples illustrates the general process for the preparation of abasic aluminum chlorosulfate (P) according to the invention.

(a) First, a slurry having the following composition was prepared:

(i) CaCl₁ 122 g

(ii) CaCO₃ 184 g

This slurry was gradually added to 1500 g of aluminum sulfate having aconcentration of 8.3% Al₂ O₃ and 0.32% OH--. The mixture was agitatedand heated to 40° C. The slurry was added over a time period of onehour, with the temperature being maintained at 40° C.

The reaction mixture was agitated under nonshearing agitation for onehour and permitted to cool to 20° C. The mixture was then maintained atthis temperature for 1/2 hour. It was then filtered under a vacuum of400 mm Hg. The filter cake was washed with 200 g of industrial water.1295 g of product were recovered, titering 8.65% Al₂ O₃ and having adensity of 1.16 and a pH of 2.6. The titer in Al₂ O₃ was adjusted to8.3% with water.

The final product chlorosulfate had the following formula:

    Al.sub.2 OH.sub.3.28 Cl.sub.1.72 (SO.sub.4).sub.0.5

Its basicity was 54.7%.

Extent of desulfation: 83%.

Proportion of polymerization by NMR=85%.

Al equivalent/Cl equivalent ratio: 3.5.

It had the following other properties:

Apparent molecular weight with 8.3% Al₂ O₃ : 24,000

    ______________________________________                                        .0.Z (Å), 8.3% Al.sub.2 O.sub.3 :                                                            1,850                                                      .0.W (Å), 8.3% Al.sub.2 O.sub.3 :                                                              950                                                      ______________________________________                                    

(b) Determination of average molecular weight and real hydrodynamicdiameters corresponding to the product chlorosulfate:

(1) Apparatus used

BECKMAN L8-55 ultracentrifuge equipped with a Ti 60 rotor:

measurement of the increment of the υ index by a BRICE PHOENIXdifferential refractometer set at the green radiation of mercury (λ=546nm);

measurements of correlation and diffused intensities by a MALVERNgoniometer, a MALVERN 253 4×4 bits channels, and an argon laser ionizedSpectraphysic model 165, capable of yielding approximately 1.5 Watt ingreen radiation (λ=514.5 nm),

(2) Mode of operation:

The basic aluminum chlorosulfate solution obtained by the processdescribed under (a) was treated in the centrifuge for 1 hr at 10,000rpm, such as to provide a clear and colorless solution The diluent waobtained by centrifugation for 100 hr at 55,000 rpm. Followingcentrifugation, a gelatinous polymer residue was observed at the base ofthe tube and the supernatant liquid diffused at an intensity in the 90°direction less than 0.5 times the intensity diffused by a benzenestandard Subsequently, samples of different concentrations were preparedby dilution with the supernatant liquid to carry out the light diffusionstudy. Each sample was first clarified by centrifugation for 1 hr at10,000 rpm.

(3) Results:

(i) υ Index increment: 0.0947 cm3/g

(ii) Average molecular weight obtained by extrapolation to zeroconcentration: 26,400,

(iii) Real average hydrodynamic diameters extrapolated to zeroconcentration:

    φZ=100 Å

    φW=65 Å

COMPARATIVE EXAMPLE 2

This example illustrates a process for the preparation of basic aluminumchlorosulfate (P₁) according to the prior art.

(a) the material of the prior art was prepared by acid attack on aluminausing a mixture of HCl+H₂ SO₄. The mixture was neutralized until a molarratio OH/Al of 1.4 was obtained and was filtered to eliminate thegypsum.

A final product having the formula Al₂ OH₂.8 CL₂.6 (SO₄)₀.3 wasproduced. The Al equivalent/Cl equivalent ratio was 2.3.

Apparent molecular weight with 8.3% Al₂ O₃ : 2,900

    φZ (Å) : 144

    φW (Å) : 85

Proportion of polymer by NMR=75%.

The product had an Al₂ O₃ concentration of 10%.

(b) Determination of M_(w) and corresponding real average diameters:

The procedure was as in Example 1(b), except for preparation of thediluent.

After 100 hr of centrifugation at 55,000 rpm, separation occurred intotwo phases having different viscosities. The phase with the lowerviscosity was separated and again subjected to centrifugation, for 60 hrat 55,000 rpm. The phase obtained via this second centrifugation wasused as the diluent.

The results were as follows:

(i) υ Index increment: 0.109 cm³ /g

(ii) Average molecular weight, by weight: 3,600

(iii) Average real diameters:

    φZ=45 Å

    φW=20 Å

EXAMPLE 3

This example illustrates the use of the chlorosulfate of the inventionfor the treatment of water.

The product (P) of the invention obtained according to Example 1 wascompared with a product of the prior art (P₁) obtained by ComparativeExample 2.

Jar-test experiments were carried out according to the following mode ofoperation:

2 Liter beaker

Ambient temperature

River Water

Jar test

(i) regulation of the pH by the addition of HCl or NaOH;

(ii) rapid agitation for 3 min after the addition of concentratedcoagulant;

slow agitation for 20 min;

settling for 15 min;

withdrawal of 400 ml;

analyses -pH;

- aluminum (atomic absorption) (HEWLETT PACKARD apparatus);

filtration - Nucleopore filter of 0.4 μm and determination of thealuminum

The water temperature was 18.3° C.; pH=7.8

Hydrometric titer=20° French

(a) In a first series of experiments, the amount of the product used wasvaried. The results are reported in Table I. The amounts of the productsP or P₁ varied from 5 to 27 g of the solution with 8.3% or 10% Al₂ O₃,respectively, per m³ of water treated.

                  TABLE I                                                         ______________________________________                                                      Aluminum (ppb in water                                                        filtered 0.4 μm)                                             Treatment dose  P.sub.1                                                                              P (of invention)                                       ______________________________________                                         5 g/M.sup.3    110     80                                                    10 g/M.sup.3    130     90                                                    17 g/M.sup.3    150    100                                                    27 g/M.sup.3    170    100                                                    ______________________________________                                    

(b) Second series of experiments

With the same amount of treatment with Al₂ O₃ (1.5 g/m³), the pH wasvaried from 7.1 to 8.45 by the addition of HCl or NaOH.

The results are reported in Table II.

                  TABLE II                                                        ______________________________________                                                        Aluminum (ppb) in water                                       pH of           filtered 0.4 μm                                            water treated   P.sub.1                                                                              P (of invention)                                       ______________________________________                                        7.1              55     40                                                    7.55             70     50                                                    8               140     90                                                    8.45            270    130                                                    ______________________________________                                    

Generally, the standard of residual aluminum was set at 200 ppb. It istherefore apparent that, with the chlorosulfate of the prior art, it isnecessary to use a pH preferably less than 8, while with thechlorosulfate of the invention, with a pH of 8.45, values are obtainedwhich are still significantly below the standard.

EXAMPLE 4

This examples illustrates the improvement provided by a process that iscontinuous, relative to the cohesion coefficient of the sludges.

(1) Preparation of the Samples:

(a) Common operating conditions:

The basicification reactors were agitated moderately using anchors suchas to maintain the homogeneity of the resulting slurry. These reactorswere maintained at a temperature of 40° C. by a water bath during thebasification period.

The final slurry was then aged at 35°-40° C. for 2 hr and cooled to 20°C. over 1 hr. The slurry was then filtered under vacuum on a polyesterfoil (vacuum of 700 mm Hg). The gypsum cake was washed with the sameamount of water in all of the experiments; the solution resulting fromthe wash was recovered in the first filtrate.

Finally, all of the products obtained were adjusted to a titer of 8.3%Al₂ O₃ in order to conduct the cohesion coefficient test of the sludges.

(b) Preparation of the chlorocarbonate slurry:

To 1 kg water, 0.739 kg anhydrous CaCl₂ was added under agitation untilcomplete dissolution, and after dissolution, 1.281 kg of ground chalkwere added having an average grain size of about 10 microns. After 2 hrof agitation, a slurry was obtained, the weight of which was adjusted to3,020 kg.

This slurry was maintained under agitation at 40° C. It was used as thebasification and desulfation reagent in the preparation of the basicaluminum chlorosulfate samples.

(c) Subsequently, chlorosulfates of different final compositions wereprepared discontinuously (samples A, B and C) and continuously (D, E andF) by the addition of appropriate amounts of chlorocarbonate slurry with2 kg aluminum sulfate at 8.2% Al₂ O₃ by weight and a basicity of 3%

(OH/3 Al×100).

The amounts of the reagents and the composition of the final productsare reported in Table III.

In the case of the discontinuous method, the amounts of thechlorocarbonate slurry were introduced over 2 hr into the aluminumsulfate.

In the case of the continuous method, one was limited for purelypractical reasons to a two stage continuous process.

In a first 3 liter reactor, over a period of 1 hr, all of the aluminumsulfate and 0.325 kg of the chlorocarbonate slurry were continuously andproportionally introduced in a manner such that the theoretical basicityof the aluminum sulfate exiting the reactor was approximately 30%.

The product which exited the first reactor was introduced into a secondreactor having the characteristics of the first reactor, together withand proportional to the amount of chlorocarbonate slurry necessary toprovide the final theoretical basicity desired.

                                      TABLE III                                   __________________________________________________________________________    Final      Corres-                                                            theoretical                                                                              ponding                                                                             Actual                                                                            Al.sub.2 O.sub.3                                                                    Slurry chlorocarbonate kg                               basicity                                                                            desulfation                                                                         basicity                                                                          content                                                                             Discontinuous                                                                        Continuous                                  Samples                                                                            desired                                                                             extent                                                                              (%) by weight                                                                           method method - 2 stages                           __________________________________________________________________________    A    52    77.5  52.2                                                                              8.89  0.558                                              B    55    82    55.2                                                                              8.55  0.590                                              C    58    86.5  58.4                                                                              8.36  0.622                                              D    52    77.5  51.6                                                                              8.41         0.325 then 0.233                            E    55    82    54.9                                                                              8.16         0.325 then 0.265                            F    58    86.5  58.2                                                                              8.62         0.325 then 0.297                            __________________________________________________________________________

(2) Performance of the chlorosulfates relative to the cohesioncoefficient of the sludges:

(a) Test used

The operating method described in Technical Handbook of Water, publishedby DEGREMONT in 1978, pages 951-952 was used.

A 250 ml test tube was used into which the sludge collected in thedifferent beakers during the flocculation test was introduced, eachbeaker having received the same amounts of the reagents.

The test tube was permitted to stand for 10 min. The excess of sludgeintroduced was then siphoned off as to leave an apparent volume ofapproximately 50 ml in the specimen.

Water was permitted to penetrate through the bottom of the test tube,with the water necessarily being the water decanted during the precedingflocculation experiment.

This had the effect of expanding the ludge and the ascending rates ofthe water corresponding to the different states of the expansion of theludge were measured.

The time T (in seconds) corresponding to the introduction of 100 mlwater for the apparent volumes V ml of the sludge equal to: 100 - 125 -150 - 175 - 200 ml was

measured. To calculate the velocity v, if Å is the height in mm of thetest tube corresponding to 100 ml (the distance between the 100 and 200ml mark on the 250 ml test tube), v is equal to (3.6 A)/T meter perhour.

The results are displayed graphically by plotting v on the ordinate andV on the abcissa, these two values being related by the equation:##EQU1## wherein: V: the apparent volume of the sludge in expansion;

v: the ascending velocity in the test tube to obtain a volume V;

Vo: the volume of the tapped sludge at zero velocity and measured on thecurve.

The coefficient K is designated the cohesion coefficient of the sludgeand corresponds to the ascending velocity in the test tube necessary toobtain a double expansion of the initial volume of the sludge.

(b) Measurements:

The water treated was a water coarsely filtered on sand, originatingfrom the river Oise.

Its temperature was 24° C.

Its pH was 8 and its turbidity 1.4 NTU.

The proportion of organic matter in mg of O₂ /1 was (determined by thepermanganate in acid medium method).

Flocculation was obtained by adding 20 ppm of the A to F sample productsunder the following conditions:

(i) 3 min rapid agitation (180 rpm)

(ii) 15 min slow agitation (50 rpm).

(iii) 20 min settling.

The DEGREMONT test of the sludges formed provided the results reportedin Table IV.

                  TABLE IV                                                        ______________________________________                                                 Discontinuous                                                                              Continuous - 2 stages                                   Samples    A       B      C     D     E    F                                  ______________________________________                                        Cohesion coeffi-                                                                         0.82    0.85   0.80  0.96  0.090                                                                              1.02                               cient of sludge K                                                             ______________________________________                                    

These results clearly show the appreciable improvement in the cohesioncoefficients of the sludges obtained by flocculation with the basicaluminum chlorosulfates obtained by the continuous method in severalstages, in particular with products of high basicity.

EXAMPLE 5

This example illustrates the improvement provided by the general processrelative to the coloration and turbidity of the products obtained.

(1) Experiment 1

This experiment illustrates the process for the preparation of a basicaluminum chlorosulfate according to the general process.

292.6 g of an industrial chalk marketed under the trademark "CALCITEC2000" by the CPC Co., were attacked with 241.2 g HCl, 33% by weight.

The sludge obtained in this manner was added gradually to 1500 galuminum sulfate containing 8.3% Al₂ O₃ and 0.32% OH--.

The slurry was added over a period of one hour under moderate agitation,at a temperature of 40° C.

The reaction medium obtained in this manner (basic aluminumchlorosulfate+gypsum) was maintained under nonshearing agitation at 40°C. for one hour.

The reaction medium was then permitted to cool to 20° C. over 2 hr,continuously under agitation.

The mixture was filtered under vacuum (400 mm Hg). The gypsum cake wasthereby separated from the filtrate. The cake was washed with water suchas to recover a basic aluminum chlorosulfate solution containing 8.3%Al₂ O₃ and having a basicity of 54.6% and a degree of desulfation of84%.

The aluminum yield was 88%.

It was determined that the solution obtained was very turbid, having aturbidity well over 100 NTU and highly colored, with a deep brown color.

(2) Experiments 2 to 5

The process followed was that of Experiment 1, but in addition:

(a) during the stage of the preparation of the chlorocarbonate slurry,5.4 g activated carbon were added, which corresponded to 3.6 kgactivated carbon per ton of aluminum sulfate to be basified.

The active carbon used is marketed under the trademark "ACTICARBONE 2S"by the CECA Co.

(b) to the reaction medium obtained after contacting the chlorocarbonateslurry with the aluminum sulfate, a nonionic polyelectrolyte flocculantwas added, polyacrylamide type (molecular weight more than 10⁶) andmarketed under the trademark "FLOERGER 920 SH" by the FLOERGER Co.

The amount of the polyelectrolyte introduced was varied, said amountbeing expressed in g/ton of the reaction medium (basic aluminumchlorosulfate mixture +gypsum) The results are reported in Table V.

                                      TABLE V                                     __________________________________________________________________________          Activated                                                                           Polyelec-                                                               carbon kg/t                                                                         trolyte g/t of                                                    No. of                                                                              aluminum                                                                            reaction                                                                             Turbidity                                                                          Coloration                                                                           Aluminum                                       Experiment                                                                          sulfate                                                                             medium (NTU)                                                                              (visual)                                                                             yield %                                        __________________________________________________________________________    2     3.6    0     40   clear brown                                                                          89.8                                           3     3.6    6     14   colorless                                                                            92                                             4     3.6   19     11   colorless                                                                            92.3                                           5     3.6   36     11   colorless                                                                            91.5                                           __________________________________________________________________________

It was noted that very little of the flocculating agent sufficed (from 6ppm) to provide an excellent result both in regard to coloration and toturbidity Furthermore, there was an appreciable improvement in thealuminum yield, amounting to a gain of 4% with respect to the product ofExperiment 1.

(3) Experiments 6 to 10

These experiments illustrate the improved process according to theinvention, using different polyelectrolytes.

The stages were carried out as in Exp. 2 to 5.

The materials used were the following:

HCL 33%: 246.5 g,

industrial chalk marketed under the trademark "STANDARD PR 2" by the BMPCo.: 298.3 g,

aluminum sulfate with 8.3% Al₂ O₃ and 0.32% OH--: 1500 g,

activated carbon "ACTICARBONE 2S": 2.5 kg/t of aluminum sulfate.

The nature and amounts of the polyelectrolytes were varied.

The polyelectrolyte trademarked "FLOCOGIL" as marketed by theRHONE-POULENC Co.

"FLOCOGIL AD 10" was a nonionic polymer comprising 100% polyacrylamide

"FLOCOGIL C 1090" was a weekly cationic copolymer containing 90%polyacrylamide and 10% ethyl-trimethyl ammonium methacrylatepolychloride.

"FLOCOGIL C 4" was a strongly cationic polymer comprising 100%ethyl-trimethyl ammonium methacrylate polychloride.

The results obtained are reported in Table VI.

It was noted that all of the polyelectrolytes provided, at least inexcess of a certain minimum amount, colorless or practically colorlessproducts with low turbidity. It was found, however, thatpolyelectrolytes of the nonionic type yielded results with the lowestamounts, which signified increased efficiency.

                                      TABLE VI                                    __________________________________________________________________________                    Grams of                                                                      polyelectrolyte                                               Experiment      per ton of                                                                             Turbidity                                                                          Coloration                                                                          Aluminum                                  No.   Polyelectrolyte                                                                         reaction medium                                                                        (NTU)                                                                              (visual)                                                                            yield, %                                  __________________________________________________________________________    6     none       0       much deep brown                                                                          72                                                                 greater                                                                       than 100                                             7     FLOEGER 920 SH                                                                           37      20   colorless                                                                           72                                        8     FLOCOGIL AD 10                                                                           49      35   colorless                                                                           76.9                                      9     FLOCOGIL C1090                                                                          100      20   practically                                                                         72.9                                                                    colorless                                       10    FLOCOGIL C4                                                                             100      40   practically                                                                         72.5                                                                    colorless                                       __________________________________________________________________________

While the invention has been described in terms of various preferredembodiments, the skilled artisan will appreciate that variousmodifications, substitutions, omissions, and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims, including equivalents thereof.

What is claimed is:
 1. A method for the treatment of impure aqueousmedia, comprising coagulating the impurities therefrom with a basicaluminum chlorosulfate of the formula:

    Al.sub.n OH.sub.m (SO.sub.4).sub.k Cl.sub.3n-m-2k

having a basicity, or ratio m/3n×100, of from about 40% to about 60%,and a ratio of Al equivalent /Cl equivalent, or ratio of 3n-3n-m-2k, offrom 2.8 to
 5. 2. The method as defined by claim 1, wherein said basicaluminum chlorosulfate has the following apparent molecular weight andapparent hydrodynamic diameters:

    MA=22,000 to 32,000;

    φZ=1,500 to 2,200 Å;

    φW=800 to 1,100 Å.


3. The method as defined by claim 1, wherein said basic aluminumchlorosulfate has the following average molecular weight M_(w) andaverage real hydrodynamic diameters φZ and φW:

    M.sub.w =10,000 to 30,000;

    φZ=90 to 450 Å;

    φW=50 to 300 Å.


4. The method as defined by claim 1, wherein said basic aluminumchlorosulfate has the following average molecular weight and averagereal hydrodynamic diameters:

    M.sub.w =19,000 to30,000;

    φZ=100 to 150 Å;

φW=60 to 80 Å.
 5. The method as defined by claim 1, wherein said basicaluminum chlorosulfate has a basicity, or ratio m/3n×100, ranging fromabout 45% to about 56%.
 6. The method as defined by claim 1, whereinsaid basic aluminum chlorosulfate has from 15 to 25% of the aluminumcontent thereof being in monomeric form.
 7. The method as defined byclaim 1, wherein said basic aluminum chlorosulfate comprises an aqueousfiltrate.
 8. The method as defined by claim 1, wherein said basicaluminum chlorosulfate has a ratio of Al equivalent/Cl equivalentranging from above 3.2 to
 5. 9. The method as defined by claim 1,wherein said basic aluminum chlorosulfate has an average molecularweight M_(w) of at least 10,000.
 10. The method as defined by claim 1,wherein said basic aluminum chlorosulfate has the following apparentmolecular weight MA and apparent hydrodynamic diameters φZ and φW:

    MA=7,000 to 35,000;

    φZ=350 to 2,500 Å;

    φW=200 to 1,200 Å.